An Evaluation of Aged and Fresh Crop Residues in No-till Cropping Systems Impacts On Soil Quality.

Productive and sustainable agriculture depends on maintaining soil quality through maintaining soil SOC content. Crop residue maintenance and management in conjunction with crop rotations in no-till systems can increase SOC content, improve soil quality, and maintain nutrient cycling which can reduce need for mineral nitrogen fertilizers. This study was conducted to evaluate the effects of aged and fresh crop residues on seven (7) no-till cropping systems on potential soil carbon (C) and nitrogen (N) additions, soil quality enhancement, and nitrogen fertilizer replacement. The residue cover from the cropping systems was sampled in spring (aged residue) and fall (fresh residue) during the 2011 growing season from the Conservation Cropping Systems Project site near Forman, ND.  The residue was weighed and analyzed for C and N content and residue dry matter yield per hectare was calculated. The seven (7) treatments were selected based on crop mixes and included crop rotations consisting of two, three, four or six crops in each rotation.  Preliminary results indicate that a corn-soybean has higher residue dry matter yield (average, 17.25 Mg ha^-1) than the other treatments. A spring wheat-winter wheat-alfalfa-alfalfa-corn-soybean rotation had the highest C and N concentrations (43% and 1.645%, respectively) of all of the treatments. For actual C and N contents in the residue, a spring wheat-winter wheat-corn soybean rotation had the  highest  C and N content of 4.23 Mg ha^-1 and 0.086 Mg ha^-1, respectively, while a spring wheat-winter wheat-alfalfa-alfalfa-corn-soybean rotation had the lowest C and N contents of  0.050 Mg ha^-1 and 1.78 Mg ha^-1, respectively.  Implications of the residue C and N contents on future fertilizer additions will be discussed.